The present invention relates to an apparatus and method for filling a hydrodynamic bearing with bearing fluid. In particular, the present invention relates to a method and apparatus for filling a hydrodynamic bearing of a spindle motor of a disc drive.
Disc drive memory storage systems include disc packs which include a plurality of stacked discs which are supported for co-rotation about a spindle shaft coupled to a base of the disc drive. A spindle is supported for rotation about the spindle shaft. A hub is rotationally coupled to the spindle to support a plurality of stacked discs for rotation.
Known disc drives include a ball bearing system for rotationally supporting the spindle relative to the spindle shaft. However, due to microscopic surface imperfections, such as rough or uneven operating surfaces, ball bearings impart vibrations to rotating discs. This vibration results in misalignment between the read and write transducers of a data head and the data tracks on the surface of the disc, thus affecting the performance and operation of the disc drive. In hard drives in portable computers, transportation of the hard drive may exaggerate the misalignment and cause damage to the ball bearings, due to vibrations and shock introduced during transport. Additionally, ball bearings are not easily sealable to smaller dimensions, thereby limiting the physical dimensions of the disc drive.
Accordingly, hydrodynamic bearings are an alternative to ball bearing systems. In the case of hydrodynamic bearings, a fluid lubricant fills bearing channels defined between the spindle shaft and spindle to support the spindle for rotation about the spindle shaft. It is important to avoid the presence of any air bubbles within the bearing channels of the bearing. The absence of air bubbles will minimize the pressure buildup inside the motor due to drops in the ambient pressure and/or thermal expansion due to increased temperature. Pressure buildup can cause the bearing to leak hydrodynamic fluid. This absence of air bubbles helps eliminate hydrodynamic fluid leakage.
Hydrodynamic fluid leakage can cause contaminants to be expelled into the disc drive which can degrade disc performance. The loss of bearing fluid can also cause increase wear to the bearing surfaces of the spindle and the spindle shaft, leading to eventual failure of the bearing. Thus, it is desirable to provide an apparatus and method for filling bearing channels of a hydrodynamic bearing where air is evacuated from the bearing channels, which is efficient and cost effective and can operate without excessive human handling.